Our understanding of the cellular and molecular pathways driving the pathogenesis in ankylosing spondylitis (AS) is still very incomplete. One of the key challenges in management of AS is lack of specific markers of disease activity. Aberrant expression of microRNAs (miRNAs) has been identified in various diseases. Recent studies demonstrated that miRNAs can be detected in the circulation and serve as potential biomarkers of various diseases. Moreover, the detection of circulating miRNAs can provide important novel information concerning diseases. At present there are no studies that have established a miRNA based signature profile in patients with AS. Given these findings, we hypothesize that patients with AS have aberrantly expressed circulating miRNAs reflective of underlying disease and inflammation and these dysregulated miRNAs can be detected through miRNA expression profiling. We further hypothesize that certain specific dysregulated candidate miRNAs in plasma of patients with AS will correlate with disease activity measures like Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). These hypotheses will be addressed in the experiments of the following specific Aims: (1) to determine the expression profile of miRNAs in plasma of patients with AS and compare it with healthy, age and sex-matched controls. (2) To test whether the expression of the specific miRNAs identified in aim-1 correlates with disease activity in AS as measured by BASDAI and ASDAS. Should the exploratory study reveal a correlation between specific miRNAs in the plasma of patients with AS and disease activity measures, they may represent potential biomarkers of disease activity in AS. These potential biomarkers of disease activity in AS can be validated in future large clinical studies and may have significant impact on management of AS.